The move so irked China's military that it laid a road on Indian territory and demanded that the tin hut be dismantled. India refused, destroyed a part of the new road and promptly raised troop numbers in the area.

Prime Minister Narendra Modi is making good on election promises of a more robust national security policy, and the fact that around 1,000 soldiers from each side are facing off in Ladakh is evidence even mighty China is not off limits.

No shots have been fired, and a brief border war between the world's two most populous nations was fought 52 years ago.

But Indian military officials said the situation in the Chumar area of Ladakh had been unusually tense in recent weeks, highlighting a simmering disagreement between the nuclear-armed neighbours that is back on the agenda at the highest level.

Modi, who swept to power in May, was unusually forthright when Chinese President Xi Jinping visited India in mid-September, challenging Xi in private on the question of incursions along their 3,500-km contested frontier.

Afterwards, he told a news conference in the presence of the Chinese leader that peace and stability on the border were needed for better economic ties Beijing has been pressing for.

P. Stobdan, a former Indian ambassador and a Ladakhi with deep knowledge of the competing claims in the region, sees a shift in New Delhi's thinking.

"The hut has become the bone of contention. The Chinese have drawn a red line. They want it demolished before they will withdraw," he said.

Last year, the Chinese forced the Indians to demolish another hut in Chumar in return for ending a face-off.

"This time the new government does not seem to be in a mood to budge," Stobdan added.

NO LONGER BUSINESS AS USUAL

Beginning in June, as it prepared to receive Xi, Modi's government set in train a series of bold actions on the border where Indian officials say China has long been nibbling away at its territory.

It ordered faster construction of 72 strategic roads along the border to narrow the gap with China's vastly superior and intricate network of roads and tracks in the mountains.

It has also rebuilt airfields, including a landing strip laid in Daulat Beg Oldi in Ladakh in 1962, the year the two countries fought their short war.

Over the past few months C-130 Hercules planes bought from the United States have been landing at the airfield some 30 km from Depsang, the site of a 21-day standoff last year when People's Liberation Army soldiers set up tents on India's side of the 1962 ceasefire line.

V.K. Singh, minister for the northeastern states, another area where the border is in dispute with China, says it is no longer business as usual on the so-called Line of Actual Control (LAC) dividing the two countries.

"Sometimes (in the past), I think for political reasons or other reasons, we would have said OK, leave it. But that perpetuates the problem, it doesn't solve the problem," said Singh, a former army chief handpicked to beef up civilian and military infrastructure in the northeast.

"You keep giving a concession, it only perpetuates the problem. So somewhere up the hierarchy someone has to say 'let's hold on'," he told Reuters in an interview about the latest confrontation with China.

India was humiliated in the 1962 war and, since then, while it has built up its conventional military and nuclear and missile capabilities, it has been careful to avoid showdowns at the border, which, despite 17 rounds of talks over two decades, remains unsettled.

Hu Zhiyong, a research fellow with the Institute of International Relations at the Shanghai Academy of Social Sciences, told China's state-run Global Times that the Modi government's moves to build up infrastructure and equipment on the Indian side of the LAC signalled a shift in posture.

"The 'offensive' strategy aims to gain more leverage in the talks," Hu told the fiercely nationalist newspaper.

HIGH-ALTITUDE HUT

The chain of events leading to the latest tensions began in Demchok, on the southeastern corner of Ladakh. On August 18, India started building an irrigation canal there as part of the government's rural jobs guarantee programme.

China protested, saying it was located inside its territory.

Then, on September 8, Indian troops erected their observation hut on a hillock in Chumar, one of the areas along the LAC where India has the tactical advantage of height.

Retired Indian army brigadier Gurmeet Kanwal, who has served in high-altitude areas, said India's position there overlooks Chinese encampments and a dirt road leading up to the area.

Beijing's response was swift. Within a day, some 500 PLA troops crossed into the area and used cranes and bulldozers to build a 2 km (1.2-mile) road.

Later that night, Indian soldiers dug up part of that road, but the Chinese have not withdrawn from the area, which New Delhi says is several kilometres inside its territory.

Around 1,000 soldiers from each side are ranged against each other, and further to the east, a group of Chinese civilians backed by the PLA intruded into the Demchok sector where India was trying to build the irrigation canal, Indian officials said.

China's public comments on the latest row with India have been measured.

"The China-India border dispute is a left-over from history. The two countries' border, to this day, has not been designated, and the two sides' understanding of the real line of control is not the same," the Defence Ministry said, adding that both New Delhi and Beijing were resolved to manage the problem.

A CIVILISED CUP OF TEA

India says China violated the ceasefire line 334 times in the first eight months of this year. Chinese officials with Xi on his visit last week said India had violated the LAC 410 times, according to an Indian government official at the talks.

Border patrols have become more frequent and probing deeper into each other's territories, officials say, often running into each other. Earlier, the two armies sent out patrols on alternating days along the most contentious areas of the border so that their troops wouldn't come into contact.

"If there is a border patrol that crosses the LAC as perceived by the other side, they are supposed to offer them a cup of tea and ask them to leave immediately. The idea is it should be civilised behaviour. At times this civilised behaviour has spun out of control with soldiers roughing each other up," said an Indian officer at the army headquarters in New Delhi.

But the head of Ladakh's local government said India had neglected the border area for decades to its own and local people's detriment. Only now was it starting to plug the gaps, he added, and that had provoked the Chinese.

"We have lost so much pasture land, grazing land over a period of time to China," said Rigzin Spalbar, chief executive councillor of the Ladakh Autonomous Hill Development Council.

"We told our people not to go close to the LAC, the area was left vacant and the Chinese sent their herders in. Now those areas have become their possessions."